There is "bipartisan skepticism" over the nuclear deal announced with Iran this week, Sen. John Thune said Thursday, indicating that there may be Democrats who refuse to follow President Barack Obama in approving the agreement.

"A lot of Democrats are keeping their powder dry and are going to listen, I think, to the discussion over the next several weeks," the South Dakota Republican, who chairs the Senate Committee on Commerce, Science and Transportation, told MSNBC's "Morning Joe" program.

"I think at the moment there is just a lot of hesitancy not only here on Capitol Hill, but around the country, as we learn more about the particulars of this and what was negotiated."

As for himself, Thune said he's trying to keep an open mind about the agreement, but "it's very hard as we learn more about it, about the concessions that were made, all the particulars of the agreement when it comes to inspections and verification. Of course, expanding this to include conventional weapons, lifting the embargo on conventional weapons and ballistic missiles is very problematic."

Iran, he continued, "is a country that terrorizes the region already" and "we're going to make it easier for them to do that by lifting the sanctions and giving them tens of billions of dollars to do it ... in addition to having access to the arms that would enable them to do that."

Thune said he intends to hear discussions and allow the Obama administration to make its case, an opportunity it will have in upcoming hearings.

There are going to be questions about when inspections can be conducted, as well as for plans to lift the arms embargo and what that will mean for the Middle East.

"Obviously that has enormous implications for Israel and our Arab allies, all of whom are extremely concerned about what this means," Thune said.

The senior senator also believes the deal makes Iran a "nuclear threshold state," as it will be able to keep some of its centrifuges and continue to do research.

"The advanced centrifuges and technology that they'll have access to going forward, and you have to remember the Iranians play the long game," Thune said. "For us, we look at these things as a matter of years, they look at decades."

Thune said he would have liked to see sanctions kept in place against Iran, as they "brought that country to its knees."

"If you read this agreement, much of the agreement particularly in the second annex is a list of all ... the individuals, the businesses, the entities are going to get sanctions relief, and the billions of dollars that's going to mean flowing into their economy, which can be turned around and used to find Hezbollah and Hamas and all of the bad things the Iranians are involved with today," Thune said.

"It's very concerning. I think we could have been in a much better place and I think we still could, but the choices are going to be somewhat limited based on what the president agreed to."

He does believe that lawmakers on both sides of the table believe in diplomacy to protect the country's national security interests, but "in this case, it's got to be strong diplomacy and strong leadership.

"That opportunity may have been lost, the window may have closed because of where we are today," he said. "But clearly, I think we would be in a much better place physically if the sanctions stayed in place, giving us an opportunity to negotiate a stronger deal which would prevent Iran from creating a nuclear capability."

Thune also fears the next president will inherit the problem of nuclear proliferation as a result of the agreement, "and that's essentially going to be the legacy of what this deal is."

Thune also discussed Donald Trump, who is at the top of many Republican presidential polls, but he thinks the real estate magnate's popularity has a short-term shelf life.

"It doesn't matter who's delivering the message, whether it's Donald Trump on the Republican side or Bernie Sanders on the Democrat side, there's a sense out there around the country of tumult, and they're tapping in to a populist streak and a lot of deep anxieties and concerns Americans have," said Thune.

"Our candidates need to speak to those issues because I think that's what's giving Donald Trump the popularity he has at the moment," he said. "Over time, when the other candidates have a chance to engage and we have the debates, the picture will become more clear and we'll have other candidates start to emerge."

There is "bipartisan skepticism" over the nuclear deal announced with Iran this week, Sen. John Thune said Thursday, indicating that there may be Democrats who refuse to follow President Barack Obama in approving the agreement.